That’s a respectable number for an odd-duck peripheral—though if it includes controllers packaged in with Steam Machines, it portends rather poorly for Valve’s living room push. I’d be surprised to see a second generation of Steam Machines, if fewer than 500,000 have sold. (That number assumes some Steam Controllers were purchased alongside Steam Links or a la carte.)
As for the tweaks, the standout is that the Steam Controller now works with your desktop, meaning there's no reason to launch Steam Big Picture if you don’t want to. You can even use the pop-up keyboard to “communicate with your non-Steam programs,” if you’re a masochist and don’t want to just use a normal keyboard.
Valve also highlighted support from third parties, including developer-created configurations for Doom, XCOM 2, and Dark Souls III, and touted “enhanced support for games purchased outside of Steam.” Oh, and the controller rumbles properly now.
Mostly this seems like a “Hey, we haven’t forgotten about the Steam Controller” post though—which is good, because six months of near-silence had me worried. Now if only we could get actual Steam Machine numbers...